Based on lessons that we have learned from the previous flight, we are
making a number of improvements in IMAPS. These changes, outlined in
sections that follow, should bring about a substantial gain in the
overall productivity of IMAPS and the quality of the data.

The observing duty factor of IMAPS on ORFEUS-SPAS I was 18.5%, and this
figure included orbits where we were commissioning the instrument and
performing trouble shooting. With the time lost in transferring data to
the Astro-SPAS tape recorder and turning on the camera for each
exposure, our highest possible duty factor could only have been (34 s
exposure interval)/(99 s interval between exposures) = 34%, a
calculation that does not account for the additional time lost during
maneuvers between targets and the inefficiencies of target
non-availability at certain times. We expect this (highest attainable)
34% on-target efficiency figure to increase to 85% with the new, much
faster (6 s) data transfer to a flash memory system (§8.2.1
below) that will be internal to the IMAPS electronics system. This
increase, when combined with the longer mission duration and the
expected performance of an undamaged photocathode, should increase our
product of observing time and effective area by a factor of about
20.